If it's a one time announcement because you took over an abandoned subreddit, a repeat post is OK. If you are posting your subreddit repeatedly to get more attention, you are a spammer, and shall be dealt with accordingly (If you see people repeatedly posting a subreddit: Report it to the mods and message us, so we can deal with it).

Can I promote any type of subreddit?

No. Here's the guidelines:

Pornography, or subreddit that frequently displays "normal" NSFW content? Yes, as long as you mark your submission as NSFW
If you submit subreddits in violation of Reddit rules, we will delete your submission, and we will report you to reddit admins.
The following topics are ineligible and results in instant and permanent bans of the submitter's account, and all subreddits the submitter moderates: Revenge porn, animal cruelty, violent/non-consentual pornography, torture porn and subreddits whose general content is NSFL.
Subreddits that are likely facing quarantine for being offensive to regular Reddit users are also ineligible.

Other places to promote your reddit:

RedditList.com - subreddit directory
MetaReddit.com - subreddit search and tools